Function compute_preflight_summary_with_runner 

pub fn compute_preflight_summary_with_runner<R: CommandRunner>(
    items: &[PackageItem],
    action: PreflightAction,
    runner: &R,
) -> PreflightSummaryOutcome

What: Compute preflight summary data using a custom command runner.

Inputs:

• items: Packages to analyse.
• action: Install vs. remove context.
• runner: Command execution abstraction (mockable).

Output:

• PreflightSummaryOutcome with fully materialised Summary data and header chip metrics.

Details:

• Fetches installed versions/sizes via pacman when possible.
• Applies the initial risk heuristic outlined in the specification.
• Gracefully degrades metrics when metadata is unavailable.